1. Field of the Invention
The present invention relates to a small display driver integrated chip (DDI) including one-chip solution; and, more particularly, to a display driver integrated circuit (IC) with a built-in memory device having a one-time programmable function.
2. Description of Related Art
A memory device having a one-time programmable (OTP) function is an internal memory device which is provided in a non-memory semiconductor IC such as a driver IC, for example, a liquid crystal display (LCD) driver IC, and has non-volatile characteristic that retains data even when power is cut off.
FIG. 1 is a plan view of a general LCD. FIG. 2 is a plan view illustrating a rear surface of a driver IC of FIG. 1 which is disposed to face a lower substrate of a liquid crystal panel.
Referring to FIGS. 1 and 2, the general LCD includes a liquid crystal panel 100, a driver IC 110 driving the liquid crystal panel 100, a driving circuit 130 controlling the driver IC 110, and a flexible substrate 120 connecting the driver IC 110 to the driving circuit 130.
The liquid crystal panel 100 includes a lower substrate 101 on which a plurality of gate lines, a plurality of data lines, a plurality of thin film transistors (TFTs) and a plurality of pixel electrodes are formed, an upper substrate 102, disposed to face the lower substrate 101, on which a plurality of color filters and a common electrode are formed, and a liquid crystal layer (not shown) disposed between the lower substrate 101 and the upper substrate 102. Herein, a polarizer 103 may be attached to the both surfaces of the lower substrate 101 and the upper substrate 102.
The driver IC 110 is a non-memory semiconductor device, and includes a gate driver, a source driver, an internal voltage generating unit, and a main logic unit. Moreover, the driver IC 110 is a memory device and includes a static random access memory (SRAM), which is a volatile memory device, and an OTP, which is a nonvolatile memory device.
The driver IC 110 is mounted on the one side of the lower substrate 101. At this point, an anisotropic conductive film 140 is attached to a plurality of electrode joining portions formed on the lower substrate 101, and the driver IC 110 and the flexible substrate 120 are mounted on the anisotropy conductive film 140 by a heat-press process.
As illustrated in FIG. 2, a plurality of output pads 111 and a plurality of input pads 112 are disposed on the rear surface of the driver IC 110. The output pads 111 are respectively connected to a plurality of electrodes formed on the lower substrate 101, and the input pads 112 are connected to the flexible substrate 120.
The input pad 112 includes a pad (see ‘A’) to which a writing voltage is applied upon OTP writing operation. Herein, the pad for an OTP writing voltage is connected to the driving circuit 130 through the flexible substrate 120. Furthermore, the disposition of the pad for the OTP writing voltage is not limited to the disposition illustrated in FIG. 2, and the pad may be disposed in a suitable disposition of the driver IC 110 according to the disposition of the OTP.
Upon OTP writing operation, the writing voltage is an external voltage, and is applied through the driving circuit 130. The writing voltage applied to the driving circuit 130 is applied to the pad for the OTP writing voltage through the flexible substrate 120. The writing voltage applied to the pad for the OTP writing voltage is applied to the anti-fuse of an OTP unit cell so that it causes the dielectric breakdown of a gate dielectric formed in the anti-fuse.
However, since the pad for the OTP writing voltage is left as a floating state after the completion of the OTP writing operation, it causes a leakage current. After the OTP writing operation, a pad for the application of an external voltage of the driving circuit 130 connected to the pad for the OTP writing voltage is separated from a power supply source supplying the external voltage so that it is left as a floating state. Accordingly, the pad for the OTP writing voltage connected to the pad for the application of the external voltage of the driving circuit 130 is also left as a floating state, thereby causing noise due to a leakage current.